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Engine knock--newly rebuilt engine


36chev
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The engine in my 36 Chevrolet has been recently rebuilt (done my brother and myself, except for machining...). After breaking in, it now has a barely audible knock or rap (my brother says inconsequential, but he hasn't really heard it) heard primarily at higher rpms. The noise unfortunately reminds me of a connecting rod knock, but it doesn't behave like the one's I've heard before. This "rap" is heard on acceleration. When I've heard rod knocks before, it is on de-acceleration--when letting off the gas. It isn't hear at all when de-accelerating or simply cruising along maintaining speed. Will a connecting rod knock only on acceleration and not at other times? At idle or slightly higher RPMs, it is quiet, so cannot test using the disconnect spark plug method (unless, as just dawned on me as typing this, take one wire off, drive on 5 cylinders and accelerate to 50 mph, and see if still hear it, would potentially take 6 tries)

The connecting rods (babbitt bearings )were set up with the shims at around 1 1/2 thousandths, maybe up to 2 thousandths using plastigauge. It has a NOS crankshaft and NOS GM connecting rods (standard size). In looking back, I've been told that one thousandths clearance would be better for intial set up. It has 10w30 oil in it.

There are only two scenarios I could see where could be a connecting rod. 1) Perhaps if one was a two thousandths clearance, it is knocking at the higher RPM. 2) Chevrolet used tubes in the oil pan to spray oil at the dippers at higher rpms. According to the Chevrolet shop manual, anytime the oil pan is pulled, one is supposed to re-align the tubes to spray directly at the dipper with a special tool I do not have. So perhaps one rod has run dry a little?

Could it be a wrist/piston pin? Do they knock more on acceleration? Would it sound like a connecting rod? After the fact, I found out that the machinist I used wasn't the best, and he fitted piston pins to the aluminum pistons (directly on the aluminum--no bushings). At least one had a tight and loose spot as it was rotated.

Any opinions? Will a connecting rod only knock upon acceleration and be primarily audible at higher rpms?

Thanks!

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I suspect that if it was a clearance issue on the rod journal, then it'd be worse before oil gets to it? Is the knock worse or less when cold, or when hot?

Seems that there is a test to check for rod knocks which involved shorting out one spark plug at a time until the noise goes away or increases? I saw something like that in an old-time repair manual for troubleshooting engine noises.

But I would suspect that any noise which is more higher-rpm related would be worse at lower rpm levels, especially under load.

What about piston clearance? Is it "in spec" too?

I don't recall engine manufacturers, in later times, changing bearing clearances to deal wtih multi-weight oil. If anything, the multi-weight should get oil into the oiling system sooner than a straight-weight 30 viscosity motor oil would. I'd check the specs on a '60s 235 Chevy 6-cylinder and see what they might be, for general principles. Most of these clearances are .0001" per inch of diameter of the bearing surface or cylinder bore, typically.

Keep us posted, please.

NTX5467

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The 10W30 oil is probably not appropriate for that engine. Single weight oil SAE 30 for summer or 20W20 for cooler weather is what it usually called for back then. Does it have good oil pressure warmed up? Dont trust that old gauge. Hook up a mechanical accessory gauge to be sure. The GM manual has the specs. The old dipper splash oil system doesn't work good unless the oil level is full or close to it. Good Luck.

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The engine in my 36 Chevrolet has been recently rebuilt (done my brother and myself, except for machining...). After breaking in, it now has a barely audible knock or rap (my brother says inconsequential, but he hasn't really heard it) heard primarily at higher rpms. The noise unfortunately reminds me of a connecting rod knock, but it doesn't behave like the one's I've heard before. This "rap" is heard on acceleration. When I've heard rod knocks before, it is on de-acceleration--when letting off the gas. It isn't hear at all when de-accelerating or simply cruising along maintaining speed. Will a connecting rod knock only on acceleration and not at other times? At idle or slightly higher RPMs, it is quiet, so cannot test using the disconnect spark plug method (unless, as just dawned on me as typing this, take one wire off, drive on 5 cylinders and accelerate to 50 mph, and see if still hear it, would potentially take 6 tries)

The connecting rods (babbitt bearings )were set up with the shims at around 1 1/2 thousandths, maybe up to 2 thousandths using plastigauge. It has a NOS crankshaft and NOS GM connecting rods (standard size). In looking back, I've been told that one thousandths clearance would be better for intial set up. It has 10w30 oil in it.

There are only two scenarios I could see where could be a connecting rod. 1) Perhaps if one was a two thousandths clearance, it is knocking at the higher RPM. 2) Chevrolet used tubes in the oil pan to spray oil at the dippers at higher rpms. According to the Chevrolet shop manual, anytime the oil pan is pulled, one is supposed to re-align the tubes to spray directly at the dipper with a special tool I do not have. So perhaps one rod has run dry a little?

Could it be a wrist/piston pin? Do they knock more on acceleration? Would it sound like a connecting rod? After the fact, I found out that the machinist I used wasn't the best, and he fitted piston pins to the aluminum pistons (directly on the aluminum--no bushings). At least one had a tight and loose spot as it was rotated.

Any opinions? Will a connecting rod only knock upon acceleration and be primarily audible at higher rpms?

Thanks!

Mr. 36 Chev.

30wt. detergent oil should be used, as Mister C9 said.

The oil clearance should be set to .002 minimum, to .002-50 maximum, as your Std. Crank size is 2.123, to 2.124.

Did you use the Plastiguage, dry, or with oil????????

Were the Rods checked for twist, Bend, and Off Set, before being installed on the pistons???????

If you would have an occasion to set the rods to .001 thousandths, that will smear the babbitt in each one!

And yes, if you had hard spots to turn in the wrist pin, to piston fit, one or more could be Galled. All Aluminum pistions have to be checked for that, it is not uncommon, at all!!!

Herm.

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Thanks for everyone's replies! According to the Vintage Chevrolet Club of America technical advisors, the connecting rods are supposed to be set up at one thousandths clearance. They said it could knock at even two thousandths! Most there also recommend using 10w30 oil for a newly rebuilt engine, and I tend to agree in theory there. The thinner oil should get to and lubricate tighter clearances better. One fellow maintains he put over 300,000 miles on a 1937 216 truck using 10w30. I could try the 30 wt, but it has the recommended oil pressure. The only thing that the oil pump does is spray oil at the rod journals at higher rpms and pump oil up to the valve rockers. Cold it will bump up to 30lbs, warm it goes to the normal 12 lbs or so at higher rpms, 7 lbs at idle.

The machinist checked the rods, and they should have all been straight since they were NOS, GM, still in the box with the factory shims. The mistake could have been using plastiguage dry--I've seen the thread here that indicates the journals should have a very light coating of oil. I'll need to find that thread again.

I am leaning towards one of the spray nozzles not being aimed correctly at the journal and perhaps starving one of the bearings, or maybe one was too tight to start with. Even though I don't have the tool, I now understand is that all I really need to do is adapt a garden hose to spray water into the oil pan central tube and see how what pattern is coming out of the individual tubes towards the oil troughs. In driving last evening it sounded like it was getting louder, and also more prominent when the engine was not under a load (kind of like I've heard with connecting rods before). I'm going to take the car to an old time mechanic to listen to today.

I'll plan on dropping the pan to check the bearings and spray pattern of the tubes, but need to drive the car about 80 miles over the weekend to get it to the workshop at my parents (had driven to my house for local show that turned out to be cancelled--discovered that fact too late!). I'll take it slow to hopefully not damage anything.

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Thanks for everyone's replies! According to the Vintage Chevrolet Club of America technical advisors, the connecting rods are supposed to be set up at one thousandths clearance. They said it could knock at even two thousandths! Most there also recommend using 10w30 oil for a newly rebuilt engine, and I tend to agree in theory there. The thinner oil should get to and lubricate tighter clearances better. One fellow maintains he put over 300,000 miles on a 1937 216 truck using 10w30. I could try the 30 wt, but it has the recommended oil pressure. The only thing that the oil pump does is spray oil at the rod journals at higher rpms and pump oil up to the valve rockers. Cold it will bump up to 30lbs, warm it goes to the normal 12 lbs or so at higher rpms, 7 lbs at idle.

The machinist checked the rods, and they should have all been straight since they were NOS, GM, still in the box with the factory shims. The mistake could have been using plastiguage dry--I've seen the thread here that indicates the journals should have a very light coating of oil. I'll need to find that thread again.

I am leaning towards one of the spray nozzles not being aimed correctly at the journal and perhaps starving one of the bearings, or maybe one was too tight to start with. Even though I don't have the tool, I now understand is that all I really need to do is adapt a garden hose to spray water into the oil pan central tube and see how what pattern is coming out of the individual tubes towards the oil troughs. In driving last evening it sounded like it was getting louder, and also more prominent when the engine was not under a load (kind of like I've heard with connecting rods before). I'm going to take the car to an old time mechanic to listen to today.

I'll plan on dropping the pan to check the bearings and spray pattern of the tubes, but need to drive the car about 80 miles over the weekend to get it to the workshop at my parents (had driven to my house for local show that turned out to be cancelled--discovered that fact too late!). I'll take it slow to hopefully not damage anything.

If you want bearings to smear, you set them at .001. If you didn't use oil on your bearing for plastigauge, you don't know where you are at on bearing clearanse.

You have a 2.125 shaft at Std., that shaft will be at least .002 thousandths bigger when hot. When that happens where is the oil going to be, there is no place, you are already a .001 thousandths short on clearance, and you still don't have the oil clearance space, so the bearing will open up to to the size that it needs for oil clearance., if it doesn't burn it out first.

Just because your rods are NOS, does not mean they are straight, and there is no way to eye ball them, you need to put them on a rod aligner, those machines, are only made for that reason.

The oil clearance you need is not going to come off the shaft, it will come off the babbitt, and what happens is the outer surface of the babbitt, meaning the surface next to the rod journal will smear. if then it does not recover, the rod burns out, and if it does recover, the smear particals go in to the oil grooving, to come loose at a later date, and you only need one sand size particle per bearing, and then start breaking up into babbitt particals, like sand, and then taking out the bearing.

I have rebuilt engine bearings of all kinds, every day for 45 years, I know how bearings work, and what makes them last.

Who ever told you to set a 2.125 bearing to .001 thousandths, and .002 thousandths would create a knock, knows nothing about engine bearings!

30 Wt. detergent is what to use in your engine, anything else just doesn't have the cushion to protect a babbitt splash bearing, if it did, I would say so.

The last thing, is your alignment tool for the pan squirt tubs. There is nothing as important. There are 3 tool pieces, to the set, for that job, somebody should have those around yet to do the complete job.

Lets, see 1937, 216 truck, with 300,000 miles, and always used 10-30wt oil, I wonder when 10-w30 came out? The way I understand it, 10W30 didn't come out untill the late 1950's, I hope your old guy is doing better now.

As a babbitter told me when he started in 1930, for the Clawson, and Balls bearing Company, he asked his boss about tight clearances, the boss told him that there were a lot of cars running around with to much bearing clearance, but there was none with to little!!!

Edited by herm111 (see edit history)
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Herm111,

Thanks again for the detailed information. Yep, I think that .001 is definitely too small. If memory serves, I think perhaps one or two may have been set at .0015, most .002 or a little more. But it sounds like should be more like .003 or so.

One fellow on the VCCA list says never to use plastigauge (he maintains will cause problems every time), but to use the old technique recommended in the 1935-36 Chevrolet Shop Manual: Take out shims until the connecting rod cannot be rapped back and forth with an 8 oz ball peen hammer, and then take out .001 shims until it can be rapped back and forth with the 8 oz hammer. This seems too imprecise to me, but I guess this was the "technique" before plastigauge.

The 1937 Chevrolet 1.5 ton truck was written up in the G&D Magazine (published by the VCCA) about 5 years or so ago. As I recall, he used it as an everyday hauling truck with the original 216 (miles were in more recent years, not over many decades). Said he had put 300,000 miles on it in using nothing but 10w30. When the engine was eventually rebuilt, I think said that the rods and mains were in good shape. Also, he said he did not use a lead additive or have hardened valve seats, but had very little valve recession.

Herm 111--What clearance would you recommend in the 36 Chevrolet, gauging with plastigauge (.002-.003 perhaps)? What is the correct technique for using plastigauge (how to coat with oil)?

I think will put some STP in it temporarily until can drive it home (about 80 miles) to check the rods. This helped a rod knock it definitely had before rebuilding with the NOS crankshaft and rods--I drove it for for two decades this way for over 25,000 miles--one journal was known to be slightly out of round. If worse comes to worse, I still have an extra 3-4 NOS GM standard sized rods that can be used. I believe the piston could be lowered enough to pull the wrist pin and put in a new rod from the bottom. The machinist checked all the NOS I have and said they were straight.

Although I took it by a shop yesterday where I know an old time mechanic, and wouldn't you know it, I could not get it to reproduce the knock! Took him for a drive, after getting the engine good and hot, still no knock! Sometimes I hear it, sometimes not. But when I do, at about 40-50 mph. But it by no means assaults the audiological senses--a barely discernable rap!

Edited by 36chev (see edit history)
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I remember seeing an article on multi-weight motor oil, in the later 1960s when 10W-50 oil was introduced. The article mentioned that with the earlier chemistry when 10W-30 was introduced, that after a 1000 miles or so, the additive package for the viscosity improver (which made the multi-weight part of things happen) would degrade and the end oil would be much closer to 10W-20 than the earlier 10W-30. I also remember seeing a recommending 30 viscosity oil for rebuilt engines as it's a more consistent-thickness oil, but as I've learned from reading various and many forum posts on www.bobistheoilguy.com, even single-weight motor oils can get thinner with use. PLUS, the viscosity rating is "a range" rather than "a specific viscosity point". Therefore, some 10W-30 motor oils might test out closer to 10W-40 and others closer to 10W-20, yet still be in the 10W-30 range. Be that as it may . . .

Plus, last time I used PlastiGage, seems that I specifically remember that it should be used ONLY on dry surfaces as any oil can "melt" it and cause eronious readings. Has something changed over the past 20 years? Other method would be to actually use a micrometer to measure the outer diameter of the crank bearing surfaces and the inside of the con-rod bearing surface, with the difference being the actual clearance. The "hammer rap" method would relate to these measurements, but as micrometers were not that common back in the earlier times, they had to come up with a general method which could be used "out in the field", so to speak, by repair shops to end up with acceptable bearing clearances.

Perhaps, I've been fortunate to be around later model engines. I was not aware that a special tool to check con-rod straightness existed? Unless an engine hydro-locked somewhere, I can't see how a lower compression engine could twist a connecting rod? I don't recall ever hearing of that happening, but I didn't know to ask about it, either.

I can understand the need for a way to correctly aim the oil tubes, though. I wonder what affect crankshaft windage might have on that situation, with all due respect?

I know that each individual engine family has their own "quirks" and "ins and outs" of how to build them to last. Babbitt bearing or not, clearances have to be "in spec" for things to work correctly. IF things get too tight, you can tell from the "heat color" on the metal where clearances were too tight. Erring on the loose end of the spec is best, but might ultimately result in shorter times between "rebuilds", yet closer clearances might extend it somewhat. BUT with the modern oils and their improved lubricity and such, even the looser settings can probably have more life than in earlier times.

Isn't there some way to convert the babbit motors to "insert bearing" motors and possibly add a real oil pump from later or heavy-duty truck engines? Just curious.

Please keep us posted on your progress.

Respectfully,

NTX5467

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, How to use.<!-- google_ad_section_end -->

<!-- google_ad_section_start -->For many years now, there are still a lot of people that don't know how to use Plastigage, to check the amount of clearance they have in a bearing they want to reset. The instructions say to clean the crankshaft, and bearing before you use the Plastigage. What they leave out is, you have to use oil, on the shaft, and on the bearing to get any kind accuracy, especially a Babbitt bearing.

If you do not use 2, or 3 drops of oil on the shaft, and in the bearing, the plastigage will not spread out to its full width, for the pressure that is put on it, from tightening the bolts. In a babbitt bearing, what normally happens is the Plastigage pushes itself in to the babbitt, and does not spread out, for a reading.

A modern engine is a little better off, as the insert is a little harder then babbitt, but you can still improve the Plastigages use, by using oil.

To remove the used Plastigage from Shaft, and Bearings, Lacquer Thinner, will take care of it fast.

Picture No. 1 Shows oil being spread on a shaft, to receive the Plastigage.

Picture 2 Shows what Plastigage looks like for some that do not do their own engines.

Picture 3 Shows, the plastigage set in the oil on the shaft, and it also keeps the Plastigage in place, while you put on the cap.

Picture 4 Shows, a cap with oil ready to be put on.

Picture 5 Shows, the Plastigage flattened out on the crank, ready to be size checked. And again, always read the crank, and not the bearing.

Picture 6 & 7 Show, Reading the Plastigage on different Journals.

Picture 8 Shows, that with oil, Plastigage does not embed in the babbitt.

Thanks Herm.<!-- google_ad_section_end -->

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Mr. 36Chev, this is the Skinny on the plastigauge. Clearance on mains, and rod bearings should be .001 thousandths per inch of shaft Minimum, and Plus .000-50 Maximum.

If you go smaller, the shaft has to fight the bearing to set it's self free, and if you go larger, you may have a bearing with to much, or wasted clearance, or a less the full bearing contact!

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Mr. NTX5467

Perhaps, I've been fortunate to be around later model engines. I was not aware that a special tool to check con-rod straightness existed? Unless an engine hydro-locked somewhere, I can't see how a lower compression engine could twist a connecting rod? I don't recall ever hearing of that happening, but I didn't know to ask about it, either.

Mr. NTX5467

Rods don't twist, bend, or off set in the motor, unless a piston would blow!

Rods, through the manufacturing, and or rebuilding process all need checked for alignment, as there is not a Rod lathe, or rod boring machine in the world that can bore a large end, with the wrist pin end of a Rod. You would think brand new rods would be aligned from the factory, and may be they are, but in 45 years of checking, I have found this not to be true.

In a modern rod with inserts, a engine shop will true a rod by taking .002 thousandths off the cap, and then use a sunnen hone to bring the rod hole back to spects, and that is fine, but there is no assurance that the wrist pin hole, and the crank hole are still aligned!

There are many machine shops that do, or don't have rod aligners, the good shops do have, and use them.

I can understand the need for a way to correctly aim the oil tubes, though. I wonder what affect crankshaft windage might have on that situation, with all due respect? "END QUOTE"

With out the pipes aligned at the dippers on the rods, they are doomed!

I am going to try to post pictures of the rod aligning machines we use.

Herm.

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Thanks Herm111 and everyone else--looks like this thread is leading to a good discussion on setting babbitt bearing clearances. I'm driving the car today, and perhaps hear a rap at certain engine speeds, but again barely heard. Also, it needs to be running for at least 1/2 hour or more before start hearing anything (if indeed I am hearing a knock...). Even though the oil doesn't need changing yet (only about 200 miles on oil change...), I think drain, will put straight 30 weight and see if that quietens any real or imagined noises. As Herm111 stated, this should probably the better weight. Does this seem like a good plan? Then, if I still imagine hearing a rap after running for a long time, will drop the pan and check clearances. From what Herm111 indicates, for the 1936 Chevrolet it should be a minimum of .002, but no more than .003.

Herm111--thanks for the detailed description and illustration of how to use Plastigauge on a babbitt bearing. Perhaps this is why modern mechanics say to use it dry (since inserts are harder), and why the VCCA folks say to use the old hammer method from the Shop Manual (because using dry, plastigauge not accurate on babbitt.)

Best regards to everyone and I'll post as anything new is discovered about the situation.

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Thanks for everyone's replies! According to the Vintage Chevrolet Club of America technical advisors, the connecting rods are supposed to be set up at one thousandths clearance. They said it could knock at even two thousandths! Most there also recommend using 10w30 oil for a newly rebuilt engine, and I tend to agree in theory there. The thinner oil should get to and lubricate tighter clearances better. One fellow maintains he put over 300,000 miles on a 1937 216 truck using 10w30. I could try the 30 wt, but it has the recommended oil pressure. The only thing that the oil pump does is spray oil at the rod journals at higher rpms and pump oil up to the valve rockers. Cold it will bump up to 30lbs, warm it goes to the normal 12 lbs or so at higher rpms, 7 lbs at idle.

The machinist checked the rods, and they should have all been straight since they were NOS, GM, still in the box with the factory shims. The mistake could have been using plastiguage dry--I've seen the thread here that indicates the journals should have a very light coating of oil. I'll need to find that thread again.

I am leaning towards one of the spray nozzles not being aimed correctly at the journal and perhaps starving one of the bearings, or maybe one was too tight to start with. Even though I don't have the tool, I now understand is that all I really need to do is adapt a garden hose to spray water into the oil pan central tube and see how what pattern is coming out of the individual tubes towards the oil troughs. In driving last evening it sounded like it was getting louder, and also more prominent when the engine was not under a load (kind of like I've heard with connecting rods before). I'm going to take the car to an old time mechanic to listen to today.

I'll plan on dropping the pan to check the bearings and spray pattern of the tubes, but need to drive the car about 80 miles over the weekend to get it to the workshop at my parents (had driven to my house for local show that turned out to be cancelled--discovered that fact too late!). I'll take it slow to hopefully not damage anything.

Mr. 36Chev.

Your crank Rod pin is 2.123, to 2.124, which is 2-1/8th inch, so while .002 minimum will work, .003 Max would be a wast of clearance. The clearance should be .002 to .002-50, but .002 if you can get it!

Now for Oil, and Plastigauge, The oil should be used on all Plastigauged bearings. The oil lets the Plastigauge spread out, with out smearing, or binding. 99 Percent our our bearings are build for other engine builders, all the ones we know use oil!

So when you hear some one say that plastigague gives a false reading, just bet that they don't know how to use it.

Thanks Herm.

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Herm111 and everyone--all the information and responses are appreciated. I'm starting to wonder if the real (or imagined according to some who have tried to listen :rolleyes:) knock or rap I hear may be from part of the valve train or still a wrist pin. It's not a clicky valve, although they do that fairly well, too, when cold. But since we used the plastigauge dry, the settings of .0015 or .002 that I thought they were at may not be true. So plan on dropping the pan to check.

I havent had a good way to listen around the engine with a stethoscope or the simple stick method--especially since it is mostly heard when on the road.

Not saying this is correct, but this weekend I was talking with a person who has rebuilt Model A engines--he said always set the rod clearance at .001. I didn't argue, but he maintained not any problems with this...

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Hello again everyone,

Mr. Herm111, you have a lot of experience with the babbitt bearing engines, including the Chevrolets that use the nozzles. So if you are willing to provide a little more advice, it would be appreciated.

Dropping the pan and then rigging up something to spray water through the tubes (I think that is what is recommended) don't think will be a problem (on ebay the special Kent-Moore tool was recently for sale, but it simply looks like a tool that could be rigged through a regular garden hose).

With the pan off, how will I know if the tubes are spraying at the correct angle to go into the connecting rod scoop? How do you align these tubes for the Chevrolet?

For the troughs and the dippers, I used the VCCA recommended method of filling the troughs with grease, turning the crankshaft backwards, and then seeing how deep the dippers went in the troughs, adjusting accordingly.

Here is a neat video showing, on a 1937 Chevy 216 (same principle as the 1936 207 engine) of oiling and spraying oil through the tubes at the connecting rods:

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With the pan off, how will I know if the tubes are spraying at the correct angle to go into the connecting rod scoop? How do you align these tubes for the Chevrolet?" End Quote"

The only way I know to make sure that you are right on the money with the settings, is to use the tools that were made for it. I took some pictures out of a book, to show what they look like. There has to be some one on the forum that has these tools. I would also try some machine shops.

Here are the pictures!

Herm.

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post-52217-143139190516_thumb.jpg

post-52217-143139190531_thumb.jpg

post-52217-143139190546_thumb.jpg

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Thanks again, Herm111. The time and knowledge you're putting toward this thread is appreciated--if there any way I can reciprocate, will be glad to do so. I had the gauge pictured in Fig. 27 of your above post for the 216 engine--but was told it wouldn't work for the older 207 oil pan. I tried in vain to trade for the earlier year gauges to no avail. I eventually sold it so that some else could use it

These things are apparently as rare as hens teeth. So if anyone has one they would like to rent out, that would be great. Perhaps your suggestion of contacting specialized rebuilders of older Chevrolet engines is an idea. When I posted to the VCCA site asking about one of these a few years ago, no luck. The tools are made out of sheet metal, so it looks like they could be copied without too much palaver.

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Don't know if this is possible with Chevy Stovebolt sixes, but if there is too much endplay in the camshaft, it can "walk" fore anb aft in the block, causing a knocking sound that sounds very much like a rod knock...

This is common with Model A Fords, which use a spring-loaded plunger to control cam end-play; the Chevrolet six uses shims under the cam retainer plate, behind thew cam gear...

With regard to the oil-pan gauges, I wonder if using the photos as a guide, you could reverse-engineer a template then make one up out of sheetmetal or even thin plywood or laminate ?

Would also think one of the VCCA guys with a set of original gauges would've created plans for a "build your own" and posted them to the site ?

Good luck with your '36 - keep us posted.

De Soto Frank

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  • 2 months later...

Been awhile, but I now have results to post about what I found out after dropping the oil pan and checking the connecting rods over the Christmas break. The car has been run about 700 miles or so after the rebuild.

In short, all connecting rod clearances are are between 1.5 and and slightly less than 2 thousandths. All bearings and journals in superb condition-no signs of scarring, marring, or lack of oil. Checked clearance with plastigauge. We used the plastigauge both with and without a light coating of oil, and really didn't find any difference in the readings. Therefore, whatever noise I hear, or more than likely imagine hearing:o, is not the connecting rods. So that is a relief to me!

Since everything on the bottom end seems to be getting plenty oil, I didn't bother trying to figure out a way to aim the oil tubes in the pan.

My best guess is that the noise I thought was hearing during hot weather and thinner oil during the break-in time could be one of two things: piston (wrist) pin--the machinist didn't fit one of them very well, and I definitely recall one piston having a tight and then loose spot when the pin was rotated in the piston; or, something in the valve train, perhaps a pushrod not perfectly true (pushrods on this long stroke engine are very long) or a valve not being as close in tolerance as could be. I tend to adjust the valves on the loose side rather than risk burning a valve.

Perhaps it was good that we dropped the pan and cleaned out the bottom--after breaking in there were the usual very fine metal particles in the oil that had settled in the bottom of the pan. This engine doesn't have an oil filter--just the screen on the oil pump pickup.

Now running 30 wt. detergent oil.

Truckmen, the oil pump is a GM NOS unit that was tight when we put it in, so don't think that would be creating any noise.

DeSoto Frank, the camshaft has a brand new bronze thrust plate (also holds the camshaft in), and we checked the clearance before putting on the timing cover. It checked out to factory recommendation (I think it was 4 thousandths). But thanks for the suggestion.

Thanks again for all the replies and advice provided through this thread!

Edited by 36chev (see edit history)
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Reading back on this post, all the attention seemed to be on the rods, either top or bottom end.

We rebuilt my Pierce engine a number of years ago, everything went back together great, with new (I think aluminum, I'm a little fuzzy on that detail) pistons from a well known supplier. About 200 miles of driving, cruising at about 35 miles per hour, and "thock thock thock" oh my gosh thought I'd burned a rod, turned engine off immediately and got my trailer to bring it home.

Pulled head and started pulling pistons, for some reason starting at number 8. Number 7 piston came out, and looked like a cheese grater had gone along the sides. Didn't hurt cylinder walls, but piston was a mess. Somehow it was not machined correctly and once it get hot it galled along the cylinder walls. New piston, double checked clearances and machine work, and now thousands of miles with nary a sound.

So, if sound gets worse at some point, you might want to check the pistons themselves.

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36 CHEV,

Many years ago one of my Chevys had an intermittant knock similar to what you describe. We droped the pan and didn't find any problem with the crank or bearings.

Eventually we noticed a slight scoring up and down the height of a cylinder wall. One wrist-pin was loose in the piston, and was sliding sideways, banging into the wall of the cylinder.

Once we replaced the piston and pin both, the noise disappeared permanently.

Marty

AACA

VCCA

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Trimcar and Marty,

When looking at the cylinder walls below the pistons as they moved up and down when the crank was turned (oil pan off), no sign of damage was evident. Cylinders still have the cross hatching from being bored. Pistons look excellent with no sign of wanting to come apart (they were old stock replacement aluminum--factory were cast iron). The wrist pins are held with a bolt clamp in the middle, and I recall torqueing those real well and using a thread lock. Also, no big metal filings in the pan or oil pickup. So I don't think either of those.

But thanks for the ideas!

Edited by 36chev (see edit history)
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Herm111,

The rods were checked out by the machinist. They are NOS (were still in the GM boxes) connecting rods--also used a NOS GM crank shaft (although it had to be straightened--over the years sitting around its own weight probably caused a slight bend). He also balanced each rod so that they would match in weight--apparently GM didn't bother to make sure they each weighed the same (although with a relatively slow turning engine, guess it probably didn't matter much). And with the pan off, there was not sign of the rods wearing unevenly from one side to the other, like there was a twist or bend.

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